What Are Watts?

By Martin Sigrist

Takeaway: Power rules when it comes to cycling performance. This article will be the first in an occasional series that will take a deep dive into exactly what watts are and how they can be improved through training. It explains what power is and how smarter workouts, using stacking, can increase efficiency giving “free” power.

Cycling is a simple sport. The fact that power meters have had such an impact on performance training is testament to this. How good you are is determined, to a very great extent, by the watts that power meters measure.

That is not to say watts are everything. Speed will depend on other numbers (also easily measured) such as aerodynamics (CdA) on the flat and weight on long climbs. Physiologically other things matter as well, most especially the ability to recover and go again after hard efforts.

But still watts are, by a long margin, the most important number.

I have previously talked about the importance of mental strength and other factors, about them being as important as physiology in terms of becoming the best that you can be. In this context I have advocated stacking as the ideal method by which workouts are conducted.

This does not mean though that I think watts are not important. If you average 200 watts you cannot “think yourself” faster than someone who averages 300 watts. Everything you do to become better on a bike has to aim at either delivering more watts or making every watt produced yield more in terms of what is important for a given target goal.

Watts rule. My point, in stressing stacking, is that achieving maximum watts requires more than just improving cellular metabolism.

So the reason that I think, for example, that it is worth spending time honing perishable skills is that doing so will mean you produce more watts more reliably (e.g. because you fatigue less).  And those watts will result in more speed (e.g. because your position on the bike is more efficient).

In order to be able to discuss this in more detail I plan to write an occasional series that attempts to do something that I do not think has been done before. Take an in depth dive looking at every factor that affects power from the production of energy at a cellular level to the actual final transfer of that energy to the bike’s chain.

This, fundamentally, is what the “fitness” side of performance training is all about and trying to improve. It really has two main goals

1. To increase the amount of energy that the muscle cells can produce over the critical period of time that an event demands.
2. To transfer as much of that energy as possible through body, to the pedals, to the cranks and then to the chain.

Doing either of the above will make you better. Doing both will make you better still.

To close this introduction, it’s just worth nailing down what power actually is.

Power is a measure of an amount of energy within an amount of time.

The basic unit of energy is a joule. A basic unit of time is a second.

One watt is one joule per second.

So increasing power means increasing the number of joules that you can produce per second. For longer times it means increasing the average number of joules that you can produce over a period of time.

However there not one but two important measures of power, from a training perspective

The first is the amount of energy that your muscle cells can produce. There is, currently, no way to measure this number directly. VO2max is an example of an indirect measure but is a surrogate and only applicable for certain exercise types.

The second is the amount of energy that you apply at some point on the bike. This can easily be measured — it’s what power meters do. Different types of power meter measure in different ways at different points. The majority do so at the front sprocket, so measure energy being applied to the chain, (e.g. through pedals, crank, spider or axle)  though some, including smart trainers, do so at the rear sprocket (so measure energy actually being applied rotate the rear wheel and make the bike move). 

The second number will always be less than the first. This is inevitable and due to the basic laws of physics. When energy is transferred some will (almost) always be lost. So if the muscles produce 100 watts, less than 100 watts will be read by a power meter. (Front sprocket power meters will read higher than rear sprocket power meters for the same reason.)

A basic opinion of mine is that, given this, it makes sense to look at the factors that could cause a loss of wattage, from cell to chain, and aim to reduce them. It is a similar approach to insulating a house. If you have a fixed heat source and want to stay warm in the depths of winter, the best approach is to plug up holes, insulate exterior surfaces and use other means to stop heat (i.e. energy) leaking outside.

A complementary opinion is that being aware of exactly what power is can help in increasing it by increasing energy production.

Stacking can help with both of these.  Indeed that it one of its main purposes: to help keep energy production high and wastage low. Just doing this it will make you better. Moreover it can be done with little extra cost or effort.

Stacking is synonymous with efficiency. It makes hours spent working out more efficient by allowing more to be achieved in the same amount of time. And it makes the key output, power, more efficient both by increasing the number of watts which are produced at the cellular level and increasing the proportion that get turned into useful “go faster” watts applied to the chain.

The bottom line is that all about the bottom line. Stacked workouts are smarter workouts. They encourage intelligent training that will yield more “pedal watts” bang per “muscle watts” buck. They can provide free watts and it would be daft not to advantage of them.  

The next article in this series will look at how a power meter works and how just knowing this can make you more powerful. I’ll go into more detail then but one key message will be that if you don’t know your cadence you are missing out on an opportunity to be a better rider.

(Email me on [email protected] if you want more info on this or any topic I have raised. I will get back to you, though it may take a few days.)

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Now among the world’s fittest sexagenarians Martin Sigrist started riding on doctor’s orders in 2005 and had to push his bike up his first hill. Next year he soloed the Tour de France. He has since experienced every form of road cycling from criterium to ultra endurance. His ongoing mission is to use the latest in science and technology to fight a, so far successful, battle against Father Time.